Centering means for cathode-ray deflecting circuits



Dec. 7, 1948. P. F. G. HoLsTl ET AL CENTERING MEANS FOR CATHDE-RAYDEFLEGTING CIRCUITS Filed oct. 2s'. 1944 Patented Dec. 7,V 1948NIT-Ensures PATENT OFFICE CENTERING MEANS FOR CATHODE-RAY DEFLECTINGCIRCUITS Paul F. G. Holst and Loren Robert Kirkwood, Oaklyn, N. J.,assgnors to Radio Corporation` of America, a corporation of. DelawareApplication october 2s, 1944, seriaiNp. 560,756

l 2 Claims.

`1 The present invention relates to cathode ray tube circuits, and moreparticularly to a novel centering means for placing the trace in thedesired location on a cathode ray indicator or image producing tube orthe like.

The principal object of the present invention is to provide a novel andsuitable centeringmeans which maintains optimum focusing of the cathoderay tube over the entire range ofadjustment provided by the circuit.

s Another object of theinventi'on is to produce a novel and reliablesource of centering voltages which is of the balanced push-pull' type,which maintains the best focus conditions regardless of the setting Vofthe centering control, and which permits the operator to displace thetrace to both sides of its center position.

Still another object of the invention is to provide a simple and efcientbalanced`4 push-pull centering means, which can be produced fromstandard, commercially available, component parts. s

Other objects and ladvantages -of the invention will, of course, becomeapparent and immediately suggest themselves to those skilled in the artto which the invention is directed from a reading of the Yfollowingspecificaticn'in connection with the accompanying drawing which shows,illustrative- `ly `and schematically, a cathode ray indicator circuitembodying the invention. i

Referring to the drawing, a cathode ray tube I of any well known type isshown as being connected to external circuits in such a manner thatseparate alternating defie'ction voltages applied to deflection voltageinput connections lor terminals I 2 and I4 will produce a traceorpattern on the flu'- orescent screen IB ofthe tube.

Electrostatic deection plates I'I and I8 deflect the electron beam' I9developed within the tube in one plane, While electrostatic" deflectionplates 2l and 22 deflect the` beam in a plane at right angles to thedirection controlled by the plates I1 and I8. The resultant: deflection'of the beam, as the voltages applied to theinput connections I2 and I4vary, causesthe beamlas it impacts upon a target area, such as the usualfluorescent or luminescent screen I5, to trace a distinctive visu-a1raster or pattern. The electron beam is produced in a wellvknown mannerby an electron gun comprising an electron source in the form of anindirectly heated cathode 24, a controlelectrode or grid 25, and anelectrode 2l which functions as an accelerating electrode. This`electrode is usuallyreferred to as .the second anode andin someinstances isin the .form of a cylinder or of a coating on the envelopeor wall of the tube. The resulting luminous spot on the cathode rayscreen IB can, in known manner, be regulated as to size and intensity bysuitable choiceof 'electrode voltages. An additional anode 28, normallyreferred to as the rst anode, cooperates with the anode 21, varying thespot size and intensity. These tube electrodes are all of usual andknown construction. To this end, the electrode 28 may be connected to aVariable potential sourcein known manner which may beadjusted to thecorrect value with respect to tbatap# plied to the electrode 21. Thevoltage applied to the second anode 2'I and its relationship to thecentering voltages for a pair of deflecting plates, for example platesII and I8, will be discussed more in detail hereinafter as itconstitutes a par-t of the present invention. Likewise. the control grid2lil is connected n known manner to a potential source which is negativewith respect yto the cathode and -is preferably made adjustable.'

. Suitable direct current sources, for example 'rectiers are connectedto terminals 29, 3l, and

32. Suitable voltages may be obtained from Ithe sections 33, 34, 65,6'6, B1, and 68 of bleeder resistor circuits connected between theterminals 29, 3l, and 32. The negative terminal 3I may be grounded orwith slight circuit modifications, which are well known to those'skilledin the art, the positive terminal 32 or some intermediate'potential asshown may be grounded so as to place the cathode 24 and the heater 36 ata high negative potential with respect to ground whereby conductingrportions in the apparatus presenting dangerous voltage can more easilybe made inaccessiblc. n

Cathode potential is provided at the junction of 61 and 68, while aVariable D. C. voltage, negative with respect to the cathode 24, for thegrid 26 'is provided at the movable armof 68. The anode 28 is als-oprovided with a variable potential positive with respect to the cathodefrom the arm of, I-B. These variable voltages are supplied to thecathode ray tube at the terminals 39 and 49, respectively.` Focusing ofthe fluorescent spot produced by the beam I9 is controlled in the usualmanner by adjustment of the ratio of the voltage on anode 21 to thevoltage on the anode 28. This may be done conveniently by Varyingthe-magnitude of the voltage applied to the terminal 40.

Regulation of the spot size and spot intensity `can be` accomplished byvarying the current to or voltage on the anode 2l. The current to theanode 2l may be increased by decreasing the bias voltage applied to thegrid 26. An increase in the anode current of the anode 21 increases theysize 56, and 69 and the potentiometer 52,

and intensity of the spot. An increase in the voltage applied to theanode 2'| increases the speed of the electrons which increases the spotintensity and may decrease the spot size. It will be understood,therefore, that the grid 26 may be reserved for modulating the beam I9if the tube is to be used for production of television images or thelike. f v

The deflecting voltages applied to the previously mentioned sets ofterminals I2 and I4 may be amplied or otherwise modied, if desirable ornecessary, in circuits 42 and 43. The circuits 42 and 43 may alsoinclude deection generators, such as oscillators for producing a desiredwave form, or other deiiection circuits, The connections I2 and I4 maythen be omitted or used only to apply control pulses. The deflectingplates and |8 are connected to the output of the amplier 42, if desired,through coupling condensers 4G and 4l. Likewise, the plates 2| and 22are connected to the output of the circuit 43 by condensers 48 and 49.It will be understood that each of the circuits 42 or 43 may compriseany suitable or special coupling network or mesh which is to beinterposed between the terminals I2 and the plates and |8, or theterminals I4 and the plates 2| and 22. In

the arrangement shown for the purpose of illustrating the invention, thecircuits 42 and 43 may be of the balanced push-pull type although one orboth may be unbalanced or single ended, if desired.

The deilecting plates 2| and 22 are connected in push-pull to thecircuit 43 through coupling capacitors 4B and 49, while centeringvoltages are supplied from a push-pull source of centering voltages.This network comprises resistors 55,

The resistors 55 and 56 are each connected at one end to the supplyterminal 32, and the free ends are connected to the ends of thepotentiometer resistor 52. The adjustable contact 'I2 of thepotentiometer 52 is connected through a resistor 69 to the terminal 29of the power supply. The plate 2| is connected to the junction of theresistor 55 and the potentiometer resistor 52 through the resistor 53,and the plate 22 is connected to the junction of the resistor 56 and thepotentiometer resistor 52 through the resistor 5|.

The resistors 55 and 55 and the resistor element of the potentiometer 52are preferably substantially equal in value, Solely by way of example,the two resistors 55 and 56 and the potentiometer resistor 52 may have avalue of one megohm each. With these illustrative values, the resistor69 will have a value of approximately 270,000 ohms,

The circuitv 43 is labeled as a vertical deflection circuit andtherefore the plates 2| and 22 serve as the vertical deilecting platesfor the tube I9.

With the arm l2 of the potentiometer 52A at the midpoint of thepotentiometer resistor c2, the voltage on each plate 2| and 22 will beequal and have a value approximately equal to one-half of the value ofthe voltage applied across the terminals 32 and 29. When the arm I2ofthe potentiometer 52 is turned until it is connected to the junctionof the resistor 56 for example, the voltage on the plate 22 will be 2%3of the voltage applied across the terminals 32 and 29, while the voltageon the plate 2| will loe 6%3 of this total Voltage. The average of thesevoltages applied to the plates is approximately equal to one half of thevoltage applied across the terminals 29 and 32 with the potentiometerarm 'I2 in its center position. With the voltages reversed by turningthe potentiometer arm I2 so that it is effectively in contact with thelead from the plate 2|, the trace is moved the same amount in the otherdirection. The circuit, therefore, produces centering voltages which maybe varied to move the beam about the center in either direction and tohave an average voltage which is approximately equal to half the voltagebetween terminals 32 and 29. Best focusing conditions are produced ifthe average of the centering voltages equals the second anode voltage.Using the centering circuit disclosed, this condition will be realized,irrespective of the position of the centering voltage control if thesecond anode bleeder, comprising the resistors 33 and 34, is so designedthat the voltage on the second anode 2'! is equal to one-half of thevoltage impressed across the terminals 32 and 29. The point ofconnection 'I4 to the bleeder circuit is selected so that the voltage onthe second anode 2'| is equal to one-half of the voltage applied acrossthe terminals 32 and 29 which, as stated, is the average voltage on thedeflection plates 2| and 22.

The amplifier 42 is labeled as a horizontal sweep amplifier by way ofexample, and therefore plates Il and I8 serve for what are normallyknown as horizontal deflecting plates whether the invention is appliedto an oscillograph, as stated above, or to an image producing tube of atelevision system or the like. The centering voltage for the plates lland IB may be obtained as shown by way of example from a centeringcircuit 1|, 6U, 6|, 62, 63, and 64. The centering voltage for the plates|1 and I8 may also be obtained in the manner disclosed and claimed inthe application of the present inventors, Serial No. 560,755, entitledCentering means for cathode ray deecting circuits, filed concurrentlyherewith.

Various modifications of the invention shown and described herein by Wayof example are possible with-out departing from the spirit and scope ofthe invention described herein, and it is desired that any and all ofsuch modications be considered within the purview of the presentinvention defined by the hereinafter appended claims. f

Having now described the invention, what is claimed and desired tobesecured by Letters Patent is the following:

1. An arrangement for providing centering voltages for the deectingplates of a cathode ray tube having means for generating a cathode raybeam and an accelerating electrode comprising a resistor combinationhaving a pair of resistors one end of each resistor being connected to athird resistor, the other ends of said pair of resistors being joinedtogether, said plates being connected to the ends of said thirdresistor, a variable contact in engagement with said third resistor, afourth resistor connected to said variable contact,

yand terminal means to provide for impressing a voltage across saidresistor combination from the free end of said fourth resistor to theends of said pair of resistors, and means to supply a relatively iixedvoltage to said accelerating electrode substantially equal to theaverage of the voltages applied to said plates.

2. Apparatus comprising an electrostatically focused cathode ray tube,said tube having a first anode, a second anode, and cooperatingdeflection plates, means for supplying a voltage to said first anode,and means for supplying centering voltages to said deflection plates,said last named means comprising a potentiometer having a resistor andanadjustable contact, a pair of resistors connected to each end of saidpotentiometer resistor, each plate also being connected to an end ofsaid potentiometer resistor, a resistor in series with said adjustableContact, and means for supplying a relatively lxed voltage to saidsecond anode substantially equal to the average of the voltages suppliedto said plates.

PAUL F. G. HOLST. LOREN ROBERT KIRKWOOD.

REFERENCES CITED The following references are of record in the file ofthis patent:

OTHER REFERENCES Mezger, Oscillograph Design Considerations, I. R. E.Proceedings, vol 27, page 197, Mar. 1939.

